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Run HAProxy on two Linux servers and use Keepalived’s VRRP implementation to move one reserved virtual IP address (VIP) between them. Clients always connect to the VIP; if the active load balancer fails its health check, the standby claims the address and begins serving the same HAProxy configuration.
This design is active-passive: only one node owns the VIP at a time. It requires identical HAProxy configurations, a shared Layer 2 network (or an explicitly supported routed VRRP design), and firewall rules that allow the nodes to exchange VRRP advertisements. The examples below use Debian/Ubuntu or RHEL-compatible systems, interface eth0, VIP 192.168.1.100/24, and two backend web servers.
What the HAProxy–Keepalived design does
HAProxy terminates client connections on the VIP and distributes requests to backend servers. Keepalived does not proxy application traffic; it manages ownership of the VIP with VRRP. The node with the higher priority becomes MASTER, while the other remains BACKUP and monitors the MASTER’s advertisements and health state.
| Component | Example value | Purpose |
|---|---|---|
| Primary load balancer | lb1, 192.168.1.101 | Starts as MASTER with priority 101 |
| Standby load balancer | lb2, 192.168.1.102 | Starts as BACKUP with priority 100 |
| Floating address | 192.168.1.100/24 | Client-facing VIP owned by one node at a time |
| Backend web1 | 10.0.0.11:8080 | Health-checked HAProxy backend |
| Backend web2 | 10.0.0.12:8080 | Health-checked HAProxy backend |
Both load balancers should use the same frontend, backend, timeout, and health-check settings. Only the Keepalived identity and priority differ. Reserve the VIP so that no host, DHCP lease, or other service can use it.
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Requirements and design decisions
- Two Linux servers on the same subnet, or a network design that explicitly supports VRRP between the interfaces.
- HAProxy and Keepalived installed on both servers.
- A VIP that is unused before Keepalived starts and is reachable by clients on the intended subnet.
- Permission to change kernel sysctl settings and manage systemd services.
- Network policy permitting VRRP advertisements between the two nodes. VRRP uses IP protocol 112; verify the exact rule syntax for your firewall or cloud network.
- The backend health URL used by HAProxy must return a success response only when the application is ready to serve traffic.
Keepalived and HAProxy releases are not pinned in this procedure. Distribution packages can differ in accepted options, defaults, service users, and validation flags, so check the man pages installed with your packages before applying a configuration to production.
Prepare both Linux servers
Allow HAProxy to bind the VIP before it is local
Because the standby normally does not own the VIP, Linux would ordinarily reject HAProxy’s bind attempt there. Enable non-local binding on both nodes:
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printf 'net.ipv4.ip_nonlocal_bind=1n' | sudo tee -a /etc/sysctl.conf
sudo sysctl -p
sysctl net.ipv4.ip_nonlocal_bindThe final command should report net.ipv4.ip_nonlocal_bind = 1. If your operating system uses a separate file under /etc/sysctl.d/, place the setting there and load that file with the system’s normal sysctl mechanism.
Install the packages
On Debian or Ubuntu:
sudo apt update
sudo apt install haproxy keepalivedOn RHEL-compatible distributions such as Rocky or Alma:
sudo dnf install haproxy keepalivedInstall the same package family and, where practical, the same versions on lb1 and lb2. Check the service names after installation; the examples assume systemd units named haproxy and keepalived.
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Configure identical HAProxy instances
Edit /etc/haproxy/haproxy.cfg on both servers. The following minimal configuration binds directly to the VIP and checks an HTTP health endpoint on each backend:
frontend fe_web
bind 192.168.1.100:80
default_backend be_web
backend be_web
balance roundrobin
option httpchk GET /health
server web1 10.0.0.11:8080 check
server web2 10.0.0.12:8080 checkAdapt the HAProxy template safely
- Replace the VIP, port, backend addresses, and health path with values from your network and application.
- Make sure the application actually exposes
/health(or your chosen path) and returns a failure status while it is unhealthy. A URL that always returns success defeats the check. - Keep this file byte-for-byte equivalent on lb1 and lb2 unless a deliberate, documented difference is required.
- Confirm that the operating-system interface carrying the VIP is the one used by Keepalived. HAProxy’s bind address and Keepalived’s VIP must refer to the same network.
Start HAProxy on each node after the configuration is in place:
sudo systemctl enable --now haproxyIf the service does not start, inspect its systemd status and logs before moving on. A syntax error, unavailable backend address, or a bind failure caused by an incorrect VIP or sysctl setting must be fixed on both nodes.
Configure Keepalived on the primary node
On lb1, create /etc/keepalived/keepalived.conf with the following values. The sample uses eth0; substitute the actual interface name shown by your operating system. The authentication value is an example shared secret; generate and protect a stronger secret for production, then use exactly the same value on lb2.
global_defs {
router_id LB_PRIMARY
enable_script_security
}
vrrp_script chk_haproxy {
script "/usr/bin/systemctl is-active --quiet haproxy"
interval 2
fall 2
rise 2
}
vrrp_instance VI_1 {
state MASTER
interface eth0
virtual_router_id 51
priority 101
advert_int 1
authentication {
auth_type PASS
auth_pass 8uQ4mN7p
}
virtual_ipaddress {
192.168.1.100/24 dev eth0
}
track_script {
chk_haproxy
}
}What each Keepalived block controls
router_ididentifies the local instance in logs and must be different on the two servers.vrrp_scriptruns the HAProxy service check every two seconds.fall 2requires two consecutive failures before the failure state is acted on;rise 2requires two successful checks before recovery is accepted.virtual_router_id 51identifies the VRRP group. It must match on both nodes and must not collide with another VRRP group on the same network.priority 101is higher than the standby’s priority, so lb1 is preferred when both nodes are healthy.advert_int 1sends advertisements at a one-second interval in this example.virtual_ipaddressdeclares the address Keepalived adds to the active interface.track_scriptconnects the service check to the VRRP instance. Without this association, Keepalived would monitor peer advertisements but would not know that a local HAProxy failure should affect ownership.
Configure the standby node
On lb2, use the same file structure, VIP, virtual router ID, authentication type, password, script, and timing values. Change the router ID, state, and priority:
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global_defs {
router_id LB_SECONDARY
enable_script_security
}
vrrp_script chk_haproxy {
script "/usr/bin/systemctl is-active --quiet haproxy"
interval 2
fall 2
rise 2
}
vrrp_instance VI_1 {
state BACKUP
interface eth0
virtual_router_id 51
priority 100
advert_int 1
authentication {
auth_type PASS
auth_pass 8uQ4mN7p
}
virtual_ipaddress {
192.168.1.100/24 dev eth0
}
track_script {
chk_haproxy
}
}Do not change virtual_router_id, the shared authentication value, or the VIP between the nodes. A mismatch prevents the two daemons from behaving as one VRRP group. The standby’s lower priority is intentional; it allows lb1 to be preferred when both are available.
Validate and start Keepalived
Validate the configuration on each server before enabling the service:
sudo keepalived --config-test -f /etc/keepalived/keepalived.confThe exact validation flag has varied between Keepalived releases. If your installed binary rejects --config-test, consult keepalived --help and that release’s man page for the equivalent check-only option. Do not skip validation merely because the file resembles a known example.
Start Keepalived on both nodes:
sudo systemctl enable --now keepalivedStart lb1 first if you want a predictable initial MASTER, then start lb2. On the primary, confirm the VIP is present:
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How failover is decided
Keepalived exchanges VRRP advertisements and evaluates the local script. The script’s interval defaults to one second when not specified; this example explicitly uses two seconds. rise and fall prevent a single transient result from immediately changing state.
The MASTER starts with priority 101 and the BACKUP with 100. A health-check failure must reduce the effective preference of the local instance or put it into a fault state so that the healthy peer can claim the VIP. Keepalived versions and documentation differ on the default script weight and on how an instance-level weight overrides a script weight. The current man page for your installed version is the authority; do not assume an older article’s default weight applies to your package.
The sample uses a process check, systemctl is-active --quiet haproxy. That catches a stopped service but can miss a process that is running yet unable to accept or route requests. For a stronger production check, use a Keepalived script that performs an authenticated or otherwise protected local HTTP request through HAProxy and exits nonzero when the response is unusable. Test any custom script separately, keep its path and permissions compatible with enable_script_security, and verify its behavior during a real failure.
Perform a controlled failover test
- Send test traffic to
192.168.1.100and verify that HAProxy reaches the expected backend servers. - On lb1, stop only HAProxy:
sudo systemctl stop haproxy. - Watch both Keepalived logs and inspect
ip addr show eth0on each node. The VIP should leave lb1 and appear on lb2 after the configured detection and election steps, normally within a few seconds but without a guaranteed downtime figure. - Confirm that new requests sent to the VIP are handled by lb2 and that backend health checks still pass.
- Restart HAProxy on lb1:
sudo systemctl start haproxy. Observe whether your installed Keepalived version preempts the standby immediately or leaves lb2 active until a policy change. Do not assume failback behavior; options such asnopreemptand their interactions are version-specific. - Repeat the exercise by stopping Keepalived, disconnecting the monitored interface in a maintenance window, and rebooting a node. Each test exercises a different failure path.
Record the observed transition time, log messages, client errors, and backend behavior. A successful VIP move alone does not prove that application sessions, TLS state, long-lived connections, or backend data remain uninterrupted.
Common failure modes and fixes
| Symptom | Likely cause | Checks and corrective action |
|---|---|---|
| HAProxy fails to start on the standby | Linux rejects a bind to the non-local VIP | Verify sysctl net.ipv4.ip_nonlocal_bind returns 1, confirm the VIP is spelled identically, and restart HAProxy after loading sysctl settings. |
| Neither node owns the VIP | Keepalived syntax, interface, or service failure | Run the release-appropriate config test, check systemctl status keepalived, inspect logs, and verify that eth0 is the real interface. |
| Both nodes claim the VIP | Split brain caused by blocked or partitioned VRRP traffic | Check firewall and network policy for VRRP protocol 112, confirm both servers can see each other’s advertisements, and consider a dedicated heartbeat network or unicast peers where the network requires it. |
| VIP never moves after HAProxy stops | The check is not tracked, the script cannot execute, or failure handling is not configured as expected | Confirm track_script names the declared script, run the script manually as the Keepalived service user, review rise/fall timing, and consult the installed man page for script-weight and fault semantics. |
| Nodes refuse to join the same VRRP group | Different virtual router ID, authentication value, interface, or network segment | Compare those fields character by character and verify that the VIP subnet and interface are valid on both hosts. |
| Traffic reaches the VIP but returns errors | Backend health endpoint, application listener, or HAProxy configuration problem | Test each backend address and health path directly, confirm the service listens on port 8080, and ensure both HAProxy files contain the same backend definitions. |
Reducing split-brain risk
Split brain is the most dangerous failure mode because two independent nodes can believe they are MASTER and answer for the same address. A simple network partition, an incorrect security-group rule, or a firewall that drops VRRP advertisements can create it.
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- Permit VRRP traffic only between the two intended nodes and monitor drops or asymmetric routing.
- Where multicast VRRP is unavailable or unreliable, use the unicast-peer configuration supported by your Keepalived version and a dedicated heartbeat path. Verify the exact syntax before deployment.
- Keep the VRRP authentication value private and identical on both nodes. Authentication is not a substitute for network isolation.
- Use monitoring that alerts when both hosts report ownership of the VIP or when neither host owns it.
- Document a manual recovery procedure: isolate one node from the client network before assigning the VIP manually, then correct the underlying partition.
Operational practices after deployment
Prevent configuration drift
Store HAProxy and Keepalived files in your configuration-management system, deploy changes to the standby first, validate them, and then perform a controlled role switch before changing the former primary. Keep the two HAProxy configurations identical unless a difference is intentional and tested.
Protect service scripts and credentials
Limit write access to /etc/keepalived/keepalived.conf and any health-check scripts. The enable_script_security setting is designed to make unsafe script execution fail rather than silently run an altered command. Replace the sample authentication value, avoid putting secrets in world-readable scripts, and review the service account and file ownership created by your distribution package.
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Plan maintenance around ownership
Before patching the current MASTER, verify that the BACKUP is healthy and that a failover has been tested. Drain or stop application traffic according to your connection-handling requirements, move ownership deliberately, patch one node, and verify it before touching the other. Because preemption and failback policies vary by Keepalived release, record the behavior observed on your exact versions and make it part of the runbook.
Limits of this pattern
Keepalived protects the load-balancer endpoint, not the backend applications or their data. A VIP can move successfully while every backend is unhealthy, while existing TCP sessions are reset, or while an upstream network remains unreachable. HAProxy’s backend checks and your application’s readiness endpoint therefore matter as much as VRRP state.
This active-passive arrangement also provides only two load-balancer nodes. It does not by itself provide geographic redundancy, database replication, automatic capacity scaling, or a quorum mechanism for larger clusters. Evaluate those requirements separately before treating VIP failover as a complete disaster-recovery plan.
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Configuration checklist
- VIP is reserved, unused, and on the intended subnet.
net.ipv4.ip_nonlocal_bind=1is loaded on both hosts.- HAProxy files are identical and the health URL represents real application readiness.
- Keepalived uses the correct interface, matching virtual router ID, matching authentication, and the same VIP on both nodes.
- lb1 has priority 101 and starts as MASTER; lb2 has priority 100 and starts as BACKUP.
- The HAProxy health script is declared and referenced under
track_script. - VRRP traffic is allowed between the nodes, and split-brain alerts are in place.
- A controlled stop-and-restart test has demonstrated VIP movement and service recovery.
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